1. Field of the Invention
The present invention relates to a pigment dispersion in which a coloring pigment or carbon black is dispersed in a medium, and a paint using the same.
2. Description of the Related Art
A coloring pigment and carbon black are used as a coloring agent in paints and printing inks and, when a coated film having a clear hue and high gloss is formed, it is necessary to use a coloring pigment and/or carbon black having a small particle diameter. However, there was a problem that a coloring pigment and carbon black having a small particle diameter are generally aggregated easily and, for this reason, they cannot be dispersed in the better dispersed state.
On the other hand, since barium sulfate has a smaller refractive index than that of other inorganic substances, and has a refractive index close to that of a coated film constructed of an organic substance, transparency can be obtained when blended in a paint, therefore, barium sulfate has been previously used as a transparent pigment. Also in barium sulfate as such the transparent pigment, it is required to blend barium sulfate having a small particle diameter. However, there was a problem that, when a particle diameter grows smaller, barium sulfate is easily aggregated and, when this is blended at a larger amount, clouding is generated in a coated film, and transparency is deteriorated.
Japanese Patent Application Laid-Open No. 2004-224949 discloses a process for preparing a composite pigment by dry-treating an organic pigment or carbon black, an organic coloring matter pigment derivative having an acidic or basic functional group or a triazine derivative having an acidic or basic functional group, and an inorganic powder such as barium sulfate. According to such the process, it is said that an organic dye derivative or a triazine derivative plays a role of mediating an organic pigment or carbon black and an inorganic powder, and a uniform composite pigment can be obtained.
Japanese Patent Application Laid-Open No. 2004-224950 discloses a process for preparing carbon black completed with an inorganic particle by adsorbing an organic dye derivative having a basic functional group or a triazine derivative having a basic functional group onto carbon black, and treating this with an inorganic particle such as barium sulfate at a pH region in which an inorganic particle has a minus surface charge.
Japanese Patent Application Laid-Open No. 2004-224949 proposes a process for preparing a composite pigment by dry treatment, but even when a composite pigment obtained by such the process is used, the sufficiently better dispersed state cannot be obtained in some cases. In addition, in Japanese Patent Application Laid-Open No. 2004-224950, since complexed carbon black is prepared in an aqueous medium, when this is added to a solvent-based paint, it must be dried once, aggregation is easily produced in a drying step and, when this is blended in a paint, the sufficiently better dispersed state is not obtained in some cases. An average particle diameter of composite pigments obtained by these prior art processes was around 400 to 800 nm when carbon black was complexed.